Many carbon nanotubes have been shown to cause lung inflammation and fibrosis, but the mechanisms responsible for these effects are not well understood. Furthermore, the ability to manufacture carbon nanotubes (CNT) in many different formats has created an urgency to develop better understanding of CNT safety and hazard ranking. We have described that CNT activated cause phagolysosomal membrane permeability (LMP) leading to release of cathepsin B and NLRP3 inflammasome activation. However, the mechanisms responsible for causing LMP and additional events controlling the inflammatory response (e.g., autophagy) are not well described, thus limiting progress in the field of nanotoxicology. The overall objective of this project is to develop well-characterized libraries of multi-walled and single-walled CNT with controlled properties (physical and chemical) that represent the most commercially viable forms and use these materials to provide insight into a mechanistic understanding and structure activity relationship of CNT toxicity both in vitro and in vivo. Our central hypothesis is that the biological responses will be dependent on specific properties of CNT and these properties regulate phagolysosomal membrane permeability (LMP) and autophagy. Furthermore, we propose that CNT cause LMP by affecting cholesterol trafficking. Therefore, we propose that we will be able to predict the proinflammatory and profibrotic activity of CNT based on these properties. The central hypothesis will be tested with the following aims: Aim 1: Develop a comprehensive library of fully characterized CNT with specific physicochemical characteristics. Aim 2: Determine the mechanism of bioactivity of CNT developed in Aim 1 and characterize the uptake, relative bioactivity of the CNT to cause LMP, NLRP3 activation (IL-1? release) and autophagy. Aim 3: Evaluate the mechanism of in vivo pathology of selected CNT. The long-term goal of our interdisciplinary team is to develop an approach to toxicity prediction based on physicochemical properties of CNT. This strategy can then be used for hazard ranking as well as safe design of the CNT forms with high commercial potential.